Month: September 2018

As you may already know if you follow me on Twitter, on Saturday September 15 I was in Ávila in the IberRadio Spanish Amateur Radio fair giving a talk about DSLWP-B. The talk was well received and I had quite a full room. I recorded my talk to upload it later to YouTube as I did last year.

Since I know that many international people would be interested in this talk and the talk was in Spanish, I wanted to prepare something in English. As I would be overlaying the slides on the video (since the video quality is quite poor and it is impossible to see the projected slides), I thought of overlaying the slides also in English and adding English subtitles.

Doing the subtitles has been a nightmare. I have been working on this non-stop since Sunday morning (as my free time allows me). I intended to use YouTube’s transcript and auto-sync feature, where you provide a transcript (in the video’s original language) and presumably an AI will auto-sync this to the video’s audio. I say presumably because in my case the auto-sync was a complete failure, so I had to resync everything by hand.

Also, since I have listened to the video over and over, I have gotten a bit bored of my own voice and noted some expressions and words that I tend to use a lot. I think this is good, because now I am more conscious when talking in public and can try to avoid using these expressions so much.

In any case, here is the final result. First you have the video with English slides:

And also you have the video with Spanish slides:

Remember that you can use either Spanish or English subtitles with any of the videos. Also, I have the translation contributions enabled, so feel free to provide subtitles in your own language if you wish.

This Wednesday, a DSLWP-B test was done between 04:00 and 06:00 UTC. During this test, a few stations reported on Twitter that they were able to receive the JT4G signal correctly (they saw the tones on the waterfall) but decoding failed.

It turns out that the cause of the decoding failures is that the DSLWP-B clock is running a few seconds late. Thus, the JT4G transmission starts several seconds after the start of the UTC minute and so the decoding fails, since WSJT-X only searchs for a time offset of a few seconds.

Ever since simulating DSLWP-B’s long term orbit with GMAT, I wanted to understand the cause of the periodic perturbations that occur in some Keplerian elements such as the excentricity. As a reminder from that post, the excentricity of DSLWP-B’s orbit shows two periodic perturbations (see the figure below). One of them has a period of half a sidereal lunar month, so it should be possible to explain this effect from the rotation of the Moon around the Earth. The other has a period on the order of 8 or 9 months, so explaining this could be more difficult.

DSLWP-B eccentricity

In this post I look at how to model the perturbations of the orbit of a satellite in lunar orbit, explaining the behaviour of the long term orbit of DSLWP-B.

Even though the cubesat LilacSat-1 was launched more than a year ago, I haven’t played with it much, since I’ve been busy with many other things. I tested it briefly after it was launched, using its Codec2 downlink, but I hadn’t done anything else since then.

LilacSat-1 has an FM/Codec2 transponder (uplink is analog FM in the 2m band and downlink is Codec2 digital voice in the 70cm band) and a camera that can be remotely commanded to take and downlink JPEG images (see the instructions here). Thus, it offers very interesting possibilities.

Since I have some free time this weekend, I had planned on playing again with LilacSat-1 by using the Codec2 transponder. Wei Mingchuan BG2BHCpersuaded me to try the camera as well, so I teamed up with Mike Rupprecht DK3WN to try the camera this morning. Mike would command the camera, since he has a fixed station with more power, and we would collaborate to receive the image. This is important because a single bit error or lost chunk in a JPEG file ruins the image from the point where it happens, and LilacSat-1 doesn’t have much protection against these problems. By joining the data received by multiple stations, the chances of receiving the complete image correctly are higher.